A friend states that since he has been taking vitamin C, he has not had a single cold. His observation has little value in assessing the effects of vitamin C because:

A. there was no control group for comparison
B. he has not calculated a correlation coefficient
C. of the effect of the observer on the observed
D. he does not specify his dosage of vitamin

Correct Answer: there was no control group for comparison ✔

Last Updated: May 03, 2024